In an image forming apparatus, a MEMS (Micro Electro Mechanical Systems) mirror is used in an optical scanning device that forms an electrostatic latent image on a photoconductive drum. The optical scanning device reciprocatingly moves the MEMS mirror and scans a laser beam radiated from a light source onto the photoconductive drum to form an image on the photoconductive drum.
In recent years, for an increase in speed of image formation on a photoconductive drum, a method of radiating a plurality of laser beams. In these methods, the optical scanning device needs to perform APC (Auto Power Control) on a plurality of light sources that radiate the laser beams. Therefore, the time required for the APC increases as the number of light sources increases. The APC needs to be carried out when laser beams are not radiated on the photoconductive drum. However, since a distance of the reciprocating movement of the MEMS mirror is mechanically determined, an effective image area sometimes decreases as the time required for the APC increases.